1. Field of the Invention
The invention concerns a process for producing fatty acyl amido carboxylic acid based surfactants.
2. The Related Art
Fatty acyl amido carboxylic acid salts are desirable surfactants. They have good water solubility, good detergency and foaming properties. Most especially they are mild to the skin. Unfortunately the amount of and extent of their usage is limited because they are expensive to produce.
The most traditional and present commercial route to fatty acyl amido carboxylic salts is found in U.S. Pat. No. 6,703,517 (Hattori et al.). Synthesis is achieved by reacting the amino acid with activated fatty acid derivatives, especially fatty acyl chlorides. The process requires a mole equivalent of alkali to remove the hydrogen chloride byproduct of the reaction. There are evident waste disposal issues with the byproducts and the added cost of chloride is not fully recoverable.
U.S. Pat. No. 7,439,388 B2 (Harichian et al.) describes a process wherein primary amido alcohol is oxidized to a corresponding amido carboxylic acid in high yield. Illustrative is the conversion of cocomonoethanolamide to N-cocoylglycine, mediated by use of a hindered nitroxide catalyst.
WO 2008/019807 A1 (Clariant International Ltd.) describes a process for preparing acyl glycinates by oxidation of fatty acid monoethanolamides using a transition group metal catalyst, particularly a gold on titanium dioxide nano-sized catalyst.
Direct esterification and interesterification are routes which also have been previously investigated. US Patent Application Publication No. 2006/0239952 A1 (Hattori) describes a reaction between a neutral amino acid and a long chain fatty acid catalyzed by an alkaline substance such as sodium hydroxide or potassium hydroxide. For instance, the reaction between glycine and lauric acid produces the acylated products lauroylglycine and lauroylglycylglycine. Significant byproducts include the non-acylated forms such as glycylglycine and glycyldiketopiperazine, as well as unreacted glycine. The reaction is said to be highly efficient (yield of the acylated forms) but this results because the ratio of lauric acid starting material to glycine is extremely high.
GB 1 337 782 (Rohm Gmbh) describes an interesterification process for the preparation of salts of N-acylaminocarboxylic acids. A carboxylic acid or an amide thereof is reacted with an aminocarboxylic acid containing at least three carbon atoms, the reaction being done in the presence of at least a stoichiometric amount (based upon the aminocarboxylic acid) of salt-forming cations. Among the aminocarboxylic acids, only glycine was said to be unusable because the process resulted in considerable resinification. Higher homologues of glycine were said, however, to react well; these included alanine, beta-alanine, sarcosine, valine, leucine, phenyl glycine and phenyl alinine. Solvents such as water or organic solvents such as dimethylformamide were said to be necessary.
DE 44 08 957 A1 (BASF AG) reports preparation of N-acyl aminocarboxylic acids by reaction of a suspension of solid anhydrous alkali metal salts of aminocarboxylic acids and an appropriate carboxylic acid or ester. Catalytic amounts of strong base are added to the suspension to promote the reaction. Illustrative is the reaction of equimolar amounts of lauric acid and anhydrous sodium sarcosine heated together molten at 200° C. in the presence of a molar equivalent of sodium hydroxide. Although the yields are high, the resultant product is highly colored.
Japanese Patent Application 57/058,653 (Ota) reports a process for producing a N-acylamino acid by reacting the corresponding amino acid with an ester. Illustrative esters include methyl laurate, methyl stearate and fatty acid glyceride esters such as triacetin, trilaurin and tristearin. Although a solvent was said not always to be necessary, all the examples utilize polar solvents such as acetonitrile, dimethyl sulfoxide or N,N-dimethylformamide.
None of the known esterification or interesterification processes are without a disadvantage. Many require relatively high temperatures and/or strong alkali to progress the reaction. These conditions promote side reactions of the amino acids with themselves rather than with the fatty acylating reagent. These competing reactions squander expensive amino acid starting reagent and require removal cleanup steps. Yields are also adversely affected. Furthermore, the necessary conditions for reaction in the known art are too harsh for the simplest of amino acids, i.e. glycine.